Photocell -to do list:
a) align the Hg lamp with the filter wheel and the photocell;
b) connect the photocell to amplifier and to the potentiometer providing the retarding voltage;
c) for every one of the six filters, measure the photocurrent vs retarding voltage; make sure you get enough data
points in the region where the photocurrent is small. There are 6 narrow bandpass interference filters
(specs here):
405nm, 436nm, 492nm, 546nm, 580nm, 692nm.
d) graph the photocurrent vs retarding voltage (six plots)
e) figure out a consistent way to determine the "stopping voltage":
- the method should be defined by a clear prescription (an algorithm) in such a way that it is reproducible, i.e.
repeated application of the same algorithm with the same parameters to the same data set should yield the
same result; (e.g. "voltage at which current begins to rise" is not meeting the reproducibility criterion)
- try at least three different methods (the third may be a variation of one of the two methods, but with different
parameter)
f) for every method, plot the found stopping voltage vs frequency and determine h from the slope (use eV as unit)
g) determine uncertainty on h (each method) and systematic uncertainties (differences) on h from method to method.
h) can you make any statement about the work function(s)?
- texts: from ch. 4 Melissinos (pdf), Princeton (pdf).
- manufacturer information: Pasco (experiment, Hg lamp), Leybold (experiment,
photo cell), lock-in amplifier (pdf)

LED - to do list:
a) connect a power supply to apply a voltage across the (LED + 100 ohm resistor);
b) use a DMM to measure the voltage across the LED, and another one to measure the voltage drop across the
100 ohm resistor (to measure the current through the LED);
c) for every one of the 6 LEDs:
- vary the voltage, starting from -0.5V to not more than 4V, but with the restriction that the LED current should
not exceed 50 mA (i.e. stop raising the voltage when the current reaches 50 mA);
- measure LED current vs applied voltage; get enough data for small LED currents (close to 0);
- graph LED current vs applied voltage (six plots);
d), e), f), g) as above
h) in your write-up, explain what happens in this experiment, and how and why the threshold voltage is related to the
frequency of the emitted light (consult appropriate references on photonics, e.g. those quoted in the manual (pdf),
or one of the websites linked below).

4. Measurement of h with LEDs
- to do list:
a) measure the room temperature with the thermometer available in the lab -- compare with the temperature reading
of the LED apparatus;
b) do measurements for at least two LEDs;
c) for every LED, obtain I-V and I-T characteristic (see users' manual below);
d) repeat the I-T characteristic for a slightly different voltage -- discuss your findings;
e) do realistic uncertainty estimates for the directly measured quantities (justify your assumptions), and assess how
this influences the uncertainty of η and h;
f) in particular, determine and quote uncertainties of slopes obtained from I-V and I-T data
g) in your write-up, explain the diode equation (where does it come from, meaning of variables, physics background)
h) quote your values (and uncertainties) for the material constant η
i) explain the material constant η. What is its significance? What value do you expect for it? Is the value that you
obtained within the expected range? What value would it have in an ideal diode?
j) your write-up should also have an explanation of how LEDs work
- manufacturer information: SVSLabs (description and manual), spectroscope manual. LEDs list: 458 nm Blue,
563 nm Green, 583 nm Yellow, 660 nm Red.
- other links: hyperphysics,
book,
wiki,
how stuff works, all about circuits,
Wisconsin.

6. Determination of the Muon Life Time
- to do list:
a) Read the manual
b) Set up the equipment following the procedure described in the manual ("Getting started", p. 29 - 30)
c) Do the "student exercises" (1) to (8) (p. 31 - 32 of the manual)
d) Use the fitter included in the software to determine the muon lifetime; in addition, extract the data into a file and do
the fitting yourself with a program of your choice. Note that there are background events in addition to the muon
decays. The distribution of background events can be assumed to be constant in time. Try to estimate the
background and subtract it before fitting to the decay time distribution. Another possibility is to use a fitting program
that allows adding a background contribution to your model.
e) quote some figure of merit fo the quality of your fit to the data (e.g. a chi squared value (χ2))
f) using your measured muon lifetime, determine the Fermi coupling constant GF.
- manufacturer information: manual (pdf), technical description (pdf)
- other links: about GF(pdf), Particle Data Group, about the manufacturer.

11. Studies of electron with a CRT
- read these notes (pdf)
- manufacturer information: PSSC document (pdf), CP06 setup (pdf), solenoid (pdf, note that the field strength
information is incorrect; you have to determine the magnetic field yourself: count the number of turns in the outermost
layer and take into account that there are three identical layers).